Machines such as, for example, on and off-highway haul trucks, wheel loaders, and other types of mobile machines are used to perform a variety of tasks. Some of these tasks involve traveling downhill along steeply graded surfaces. This downhill travel may accelerate movement of the machines. This acceleration may be substantial and may cause damage to the machines. The damage may be avoided by appropriately retarding movement of the machines. Unfortunately, it may be possible to over-retard movement of the machines, causing the machines to move slower than necessary, thereby reducing efficiencies of the machines, or to under-retard movement of the machines, allowing the machines to move too quickly, thereby over-speeding and damaging drivetrains of the machines.
One way to avoid the over-retarding and/or under-retarding of the movement of machines may be to automate the retarding of the movement of the machines. An example of this strategy is described in U.S. Pat. No. 6,349,253 (the '253 patent) issued to Bellinger on Feb. 19, 2002. The '253 patent describes a system for controlling downhill operation of a vehicle. The system includes a controller operable to control an engine compression brake of the system, a wastegate of a turbocharger of the system, a service brake of the system, and/or a transmission of the system. In particular, the controller regulates the engine compression brake directly to provide a discrete amount of engine retarding torque; the wastegate to modify this amount of engine retarding torque; the transmission to select a gear ratio, which further modifies the amount of engine retarding torque; and/or the service brake to retard wheel motion.
When a speed of the vehicle of the '253 patent is decreasing and below a target speed (i.e., the vehicle is over-retarded) or increasing and above the target speed (i.e., the vehicle is under-retarded), the controller adjusts the amount of engine retarding torque. The controller downwardly adjusts the amount of engine retarding torque by directly controlling the engine compression brake, and then by adjusting the wastegate. Once the controller minimizes the amount of engine retarding torque (by controlling the engine compression brake directly and/or by adjusting the wastegate), the controller deactivates the engine compression brake and ceases controlling the wastegate if the vehicle is still over-retarded. The controller upwardly adjusts the amount of engine retarding torque by adjusting the wastegate, and then by directly controlling the engine compression brake. Once the controller maximizes the amount of engine retarding torque (by adjusting the wastegate and/or by controlling the engine compression brake directly), the controller downshifts the transmission to further increase the engine retarding torque if the vehicle is still under-retarded. Specifically, the controller activates the service brakes, downshifts the transmission, deactivates the service brakes, deactivates the engine compression brake, and adjusts the wastegate to a default setting. The adjusting of the wastegate, direct controlling of the engine compression brake, and downshifting of the transmission are then repeated until the vehicle is no longer under-retarded.
Although the system of the '253 patent may help reduce the under-retarding and/or over-retarding of the vehicle of the '253 patent, the system may do little to maximize continuity of the amount of retarding of the vehicle of the '253 patent. Specifically, the controller of the '253 patent may do little to smooth the decreases and/or increases in retarding torque provided by the engine compression brake as the controller directly controls the engine compression brake to provide discrete amounts of engine retarding torque. Thus, the vehicle of the '253 patent may experience rough accelerations and/or decelerations as the engine retarding torque abruptly increases and/or decreases.
The disclosed method and system are directed to overcoming one or more of the problems set forth above and/or other problems in the art.